Lesson 3: CAD Modeling Fundamentals for CEM Simulations

In this lesson, we'll explore the foundation of building accurate models for your FDTD simulations: Computer-Aided Design (CAD) modeling. We'll discuss user-friendly CAD software options and essential techniques for creating 3D models of microwave components.

Why CAD in CEM?

Accurate representation of the geometry is crucial for successful FDTD simulations. CAD software allows you to:

• Design complex 3D models: Microwave components often have intricate shapes. CAD software provides tools for creating these shapes precisely and efficiently.
• Ensure model closure: For FDTD simulations, the model needs to be "watertight," meaning it has a closed surface without any holes or gaps. This is essential for proper mesh generation (covered in a future lesson).
• Define material properties: Certain CAD software allows assigning material properties to different parts of the model, which can be directly incorporated into the FDTD code.

Choosing a User-Friendly CAD Software:

There are many CAD software options available, but some are more beginner-friendly and suitable for our purposes:

• FreeCAD: A free, open-source, and powerful parametric CAD software. It offers a wide range of features, including 2D sketching, 3D modeling tools, and mesh generation capabilities (although we'll use Gmsh for meshing in this course). https://www.freecad.org/ https://www.youtube.com/watch?v=NXN7TOg3kj4&list=PLWuyJLVUNtc0UszswD0oD5q4VeWTrK7JC
• OpenSCAD: Another free and open-source software focused on creating solid models through text-based scripting. It's particularly well-suited for designing parametric models with repetitive features. https://openscad.org/ https://www.youtube.com/watch?v=dx06_gcdMck&list=PL3by7evD3F51u-17hoepe7IduGkfp2Fu6

Basic CAD Modeling Techniques:

Let's delve into some fundamental techniques for building 3D models in CAD software:

1. 2D Sketching: Most CAD software utilizes 2D sketches as the foundation for creating 3D models. You can draw lines, circles, arcs, and other shapes to define the basic geometry.
2. Extrusions: This operation allows you to extrude a 2D sketch into a 3D solid object by specifying a distance or depth.
3. Revolves: By revolving a 2D sketch around an axis, you can create cylindrical or disc-shaped objects.
4. Booleans: Boolean operations like union, difference, and intersection allow you to combine existing 3D models to create more complex geometries.
5. Sweeps: Sweeping a 2D profile along a path can generate objects with varying cross-sections, useful for tapered waveguides or horn antennas.

Tips for Modeling Microwave Components:

• Start simple: Begin with basic shapes like cubes, cylinders, and spheres before progressing to more complex geometries.
• Parametric modeling: Utilize parametric features whenever possible. This allows you to easily modify dimensions later without rebuilding the entire model.
• Unit system: Maintain a consistent unit system throughout your model (e.g., millimeters) to ensure compatibility with meshing software and FDTD code.
• Watertightness: Double-check your model for any gaps or holes. Ensure proper closure for successful mesh generation.

Practice Makes Perfect:

The best way to master CAD modeling is through practice. Start by creating simple microwave components like waveguides or rectangular cavities. As you gain confidence, explore more intricate designs.

Beyond This Lesson:

While these basics equip you to create fundamental models, advanced techniques like lofting and surface modeling can be explored for even greater design flexibility.

Next Steps:

In the next lesson, we'll do a deeper dive in CAD and 3D modeling. Remember, a well-designed and accurate model is essential for obtaining reliable results from your FDTD code.